Inconsistency when setting TextView font size in code and in resources

The official documentation does not seem to answer this, or I can't figure it out.

Element (nevermind the AlertDialog, it happens on any TextView as well):

TextView tv = (TextView) dialog.findViewById(android.R.id.message);

Inconsistency. Case A:

tv.setTextSize(TypedValue.COMPLEX_UNIT_SP, 14);
// or tv.setTextSize(14); does the same

Case B:

tv.setTextSize(getResources().getDimension(R.dimen.text_size_small));
// TypedValue makes no difference either.

where values/dimens.xml has it:

<dimen name="text_size_small">14sp</dimen>

Result: font size is not the same, and appears much bigger when retrieving from resource. I'm probably missing something, so what's my mistake, and the most important: why?

-- UPDATE TO FIRST ANSWER --

The fixed number was just an example, as nobody would hard code fixed font sizes in code. So let me rephrase the question:

Why if I get the resource from code, the text size is bigger than when I get the resource from a XML layout? Besides, the question is still the same: how do I retrieve a 14sp unit in code and keep it consistent with the 14sp unit that is set in the layout XML? I did not accept the answer because it does not tell me how to use sp units from resource in code for text size.

On this layout, the font size is different, even if the dimension is the same:

<TextView
            android:id="@+id/my_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            style="@style/TextBody" />

styles.xml:

<style name="TextBody">
    <item name="android:textSize">@dimen/text_size_small</item>
    <item name="android:lineSpacingMultiplier">1.1</item>
    <item name="android:textColor">@color/body_text_1</item>
    <item name="android:textIsSelectable">true</item>
    <item name="android:linksClickable">true</item>
</style>

See text_size_small there? Why in this case the font size is smaller than in the code, using the same dimen resource?

You should use setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize); because the documentation of the getDimension method states that it returns a Resource dimension value multiplied by the appropriate metric. which I understand to be the precalculated absolute px value.

That is, use:

tv.setTextSize(TypedValue.COMPLEX_UNIT_PX, getResources().getDimension(R.dimen.text_size_small));

Somehow this seems to fit:

XML:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="typo14">9sp</dimen>
</resources>

Java:

setTextSize(TypedValue.COMPLEX_UNIT_SP, 9);
setTextSize(TypedValue.COMPLEX_UNIT_PX, getResources().getDimensionPixelSize(R.dimen.typo14));